Impact wrench



Patented Mar. 20, 1945 Clifford E. Fitch, Bryan. Ohio, assignor to The Aro Equipment Corporation, Bryan, Ohio, a con.

poration of Ohio Application May 1,8. 1942, Serial No. 443,443 1s claims. `(ci. 19a-30.5)

My present invention relates to an impact tool or wrench of the rotary type wherein an electric or pneumatic motor drives the wrench head in synchronism with the motor as long as there is no appreciable resistance to rotation but which, after predetermined resistance to rotation is encountered, operates further to impart rotary impact blows for driving a bolt or nut to tightened position.

One object of the invention is to provide an impact wrenchof this character, which is of allmetal construction and simple and inexpensive to manufacture.

A further object is to provide an impact wrench of the rotary type wherein the wrench rotates the work until the work sets up a resistance torque greater than the rotating driving torque and then delivers a series of impacts to overcome the resistance torque of the work through the medium of spring-urged shoes which normally rotate between a rotary hammer plate and the housing of the device, but when the resistance torque increases to a predetermined extent, the shoes become cocked against the bias of the spring to effect a disengagement of clutch lugs of the rotary hammer 'with respect to clutch lugs of a rotary anvil, after which the impact operation occuis.

Another object is to provide the spring so arranged with relation to the shoes that it permits the shoes to be cocked during only a small angular movement of the hammer with additional power for the impact blow being built up behind the vanes of a driving motor of pneumatic type. Still a further object is to provide a simple type ofdrving mechanism which is sturdy and eilicient, and does not require frequent repair or replacement of parts.

With these and other objects in view, my invention consists in the construction, arrangement and combination of the various parts of my impact wrench whereby the objects contemplated are attained, as hereinafter more fully setl f through an impact wrench embodying my invention, showing the driving mechanism associated with an end plate and a shaft of a driving motor; Figure 2 is a horizontal sectional view on the line 2-2 of Figure 1, showing the coaction of clutch lugs of a hammer member m'th clutch lugs of an anvil member;

Figure 3 is a sectional view on the line 3--3 of Figure 2, omitting the housing of Figure 1 and showing only the main portion of the driving mechanism in normal position, as when a bolt or nut is being tightened, without offering substantial resistance to rotation;

Figure 4 is a similar sectional view showing the bolt or nut offering resistance torque to such an extent that the hammer has become disengaged from the anvil preparatory to rotating to a position for delivering an impact blow; and

Figure 5 is a fragmentary view similar to a portion of Figure 4 and showing a modification.

On the accompanying drawing I have used the reference numeral I0 to indicate the bottom end plate of 'a pneumatic motor, such as one of the vane type. The motor has a shaft I2 for driving the mechanism of my impact wrench. A lbearing I4, such as one of the ball type, is shown for journaling the shaft I2 in the end plate III. The shaft I2 acts as a prime mover for my irnpact wrench, the construction of which will now be described.

My impact wrench includes a housing I6 which may be secured to the end plate I0 of the motor, as by bolts 20 passing through an annular flange I3 of the housing. The vhousing I6 has in its lower endl a bushing 22 in which an anvil or wrench shaft 23 is rotatably mounted. The anvil or wrench shaft 23 may have a squared lower end 2| on which a socketv member 24 may be secured, as by a pin 25, or may be of any suitable construction for coaction with thework to be rotated by the impact tool.

Between the motor shaft I2 and the anvil or wrench shaft 23 is an arbor 26 operating as a driving shaft, as will hereinafter appear. 'Ihe arbor 25 has a splined connection 28 with the motor shaft I2 at its upper end, and is aligned with the wrench shaft 23 at lits 'y lower end by means of a pin 24a. The arbor 26 has a flange 3i) thereonwhich may be formed integral therewith, as illustrated. Slidable on the arbor or shaft 26 is a sleeve 32 having a flange 34 at its upper end.

A coil spring 36 is interposed between the iianges 30 and 34.

The lower end of the sleeve 32 rests on a hammer member or plate 38 which is slidable and rotatable on the shaft 26. The hammer Vplate 38 normally rests at its center against an anvil plate or head 42 of the wrench shaft 23. The spring 36 exerts a predetermined pressure for tending to keep the hammer plate 38 tightly against the anvil head 42 and the lower end of the sleeve 32 tightly against the hammer plate.

The hammer plate 38 is provided with a pair of opposite clutch lugs 40 adapted to coact with companion clutch lugs 44 on the anvil plate 42, as shown 1n Figure 2. The hammer plate lugs 40 have forward faces 4l engaging, at times, rearward faces 45 of the anvil lugs 44.

An opposition plate or thrust bearing 55 is located below the hammer plate 38 and is suitably supported in a recess of the housing I6, as shown in Figure l. A pair of oppositely disposed shoes 54 is adapted to freely slide on the plate 55, and these shoes have upwardly extending bifurcated arms 52. The arms extendvthrough slots 58 of the hammer plate 38, which slots have enlarged parts 56 to accommodate the shoes 54. The bifurcated arms 52 have a cross-pin 46 therethrough, which cross-pin passes through a perforation 48 of the arbor or drive shaft 26. To permit sliding of the sleeve 32 along the shaft 26, the sleeve is provided with a pair of slots 50 to accommodate the pin 46.

In Figure 5 I show a ball 55b for a modified form of opposition plate 555. An annular series of the balls 55h forms a rolling thrust bearing for the shoes 54 to reduce energy loss and heating by friction.

Practical operation In the operation of my impact wrench the clutch 24 may be applied to a bolt or nut, and the motor shaft l2 then rotated by introducing compressed air to the driving motor. As long as no appreciable resistance is offered to rotation by the bolt or nut, the spring 36 will keep the hammer plate 38 in its lower and fully engaged position with respect to the anvil head 42. The rotation of the shaft 26 will be imparted through the cross-pin 46 to the bifurcated arms 52 of the shoes 54 and merely slide the shoes around on the opposition plate 55, carryingy with them the hammer plate 38. In the case of Figure 5, the opposition plate 55 will be rotated by friction from the shoes 54 and roll on the ball bearing 551.

When resistance torque is encountered, however, the driving torque still being applied will result in the pin 46 tilting the shoes 54, as shown in Figure 4, causing the shoes to become cocked or tipped to an angular position between the hammer plate 38 and the opposition plate 55. The degree of such'tipping will depend upon the resistance torque'balanced against the compression of the spring 36. As long as theresistance torque is below a predetermined amount, the hammer plate 38 will remain engaged with the anvil head 42, but as the resistance torque increases, it will iinally become great enough to compress the spring 36 to the position of Figure 4. In this position the shoes 54 have tipped far enough so that the lower left edge of the shoe will ride on the opposition plate 55, and the upper right edge of the shoe will engage a shoulder 60 of the slot enlargement 56, thereby raising the hammer plate 38 toa position where the lower surfaces of its clutch lugs 46 will clear the upper surfaces of the clutch lugs 44 of the anvil head 42. Such clearance has just occurred in Figure 4, and, thereupon, the hammer plate 38 will rotate further, leaving the anvil head behind, the shoulders 4I, for instance, traveling, as vindicated by the arrows A in Figure 2, to a new position against the next successive shoulders 45. The lugs 46 have then rotated 180 degrees,

The driving motor approaches a stall during the period of cooking of the shoes 54, and since it is a pneumatic motor, builds up a high air pressure behind the rotor blades. After the hammer plate is released from the anvil head, this stored up pressure tends to accelerate the hammer to a very high velocity, thereby increasing the impact effect of the lugs 40 on the lugs 44. The repeated impact operation delivers a series of impacts to the work, and the operator soon becomes experienced in knowing how long to leave the tool operating with impact for tightening the work to the desired degree.

The parts of my impact wrench are symmetrical, so that thev wrench is adaptable to run and impact in either direction. This makes it useful for the purpose of removing bolts and nuts that are tight, as well as for the purpose of installing them as in the assembly of machinery.

My wrench is so designed that the shoes 54 operate effectively to cause impact blows to be imparted, as well as ordinary rotation of the tool when there is little resistance to rotation. The shoes are not subject to excessive wear, and, being symmetrical in shape, may be reversed when Wear has occurred, as when the tool is operated for rotation in one direction more than in the other. Reversal of the shoes substantially doubles their life Where the tool is used only in one direction. 'I'he parts are relatively easy to disassemble and replace, and the housing I6 entirely encloses the operating parts to avoid entrance'of dirt into the operating mechanism.

Some changes may be made in the construction and arrangement of the parts of my device without departing from the real spirit and purpose of my invention, and it ismy intention to cover by my claims any modified forms of structure, or use of mechanical equivalents, which may be reasonably included within their scope.

I claim as my invention:

1. In an impact wrench, a motor driven shaft,

. a wrench shaft and an operative connection between said shafts comprising an anvil carried by said wrench shaft, a hammer for'driving and impact coaction therewith, said anvil and hammer having interengaging lugs, and means for driving said anvil from said hammer so that recurrent interruption and re-establishment ofl said lugs occurs upon a predetermined resistance of the work to torque comprising means biasing said hammer toward engagement with said anvil, said hammer having an opening therethrough, a separating member, an opposition plate for said separating member to slide on,'said separating member including a driving arm through said opening, said motor driven shaft having a projection coacting with said arm to cock said separating member between said opposition plate and said hammer and thereby cause it to move said hammer away from said opposition plate to thereby vseparate the lugs of said hammer from the lugs of said anvil upon such resistance to torque being offered.

coaction therewith, said anvil and hammer havdriving torque for said wrench shaft, said last means comprising ,a spring biasing said hammer toward engagement with. said anvil, said hammer having openings therethrough, declutching elements having projections to bear against said housing and said hammer, said declutching elements including arms extending through said openings, said motor driven shaft having projections pivotally and slidably coactingwith said arms to cock said declutching elements and thereby cause them to lift said hammer away from said housing to disengage the clutch lugs of said hammer from the clutch lugs of said anvil upon such resistance to torque. being offered to the rotation of said wrench shaft.

3. In a tool of the character described, a pair of rotatable members having axes extending generally in the same direction, means releasably engaging the two members intermittently including engageable faces generated normal to theangle of approach of said twomembers as they move into engagement, means for effecting intermittent release and engagement of said engageable faces by relative movemnt of said members axially,` means to impart energy to one of said members, means to transmit energy intermittently to the other member upon re'engagement of said engageable faces, said last means comprising an opposition plate in opposition to said iirst member, shoes between said first member and said opposition plate, and torsional means connected with saidv shoes laterally therefrom to effect cocking of the shoes between said member and'plate to disengage said engageable faces.

4. In a tool of the character described, a housing, a rotary tool head and a rotary hammer jour'- nalled in said housing, coacting releasable impact clutch members on said hammer and head, rigid means interposed between said hammer and a portion of said housing and Ladapted to disengage the clutch members whereby the head remains stationary during a partial revolution of the hammer followed by -an impact blow imparted to the head, a spring tending to urge said hammer to engage said head and to normally maintain said clutch membersin engagement, and driving means so connected with said rigid means 6. In a rotary impact tool having an anvil and a hammer for striking the anvil, clutch members on the hammer and anvil disengageably cooperating, a spring to normally hold said clutch members in engagement, driving means for the hammer, and means connecting the hammer and driving means when the clutch members are engaged, and adapted to disengage said clutch members when the driving means is incapable of driving the anvil comprising a slide plate in opposition to said hammer, shoes rotatable with said hammer and interposed between it and said thrust plate,

-' and means for driving said hammer` by driving said shoes, said last means being Lconnected with a prime mover and being plvotally and slidably engageable with said shoes at points spaced laterally therefrom. thereby to effect a change inv the angular position of the shoes upon predetermined driving torque of the prime mover 'in excess of resistance to turning torque of the work.

7. In an impact wrench, a housing, a drive shaft projecting into said housing, a wrench shaft projecting from said housing and an operative connection between said shafts comprising a rotary anvil carried by said wrench shaft, a rotary hammer for driving and imp-act coaction therewith, said anvil and hammer-having clutch lugs for mutual engagement, and means tending to disegage said clutch lugs from one another when predetermined force opposes rotation of said wrench shaft, said last means comprising a spring biasing said hammer toward engagement with said anvil, an opposition platecarried by said housing, shoes located between said hammer and said opposition plate, said shoes including arms extending" laterally therefrom, said drive shaft having a cross-pin vcoacting with said arms to lcock said shoes and thereby cause them to lift said hammer away from said opposition plate when such predetermined force opposes rotation of said wrench shaft.

8. A device for accumulating torsional force in an impact tool comprising a pair of end members mounted for relative axial movementy resilient means interposed between said end members and operable to resist movement of said end members toward each other, a thrust plate beyond one of said end members, shoes slidable thereon and i interposed between said one of said end members and said thrust plate, said one of said endY memf bers constituting a rotary hammer, a rotary anvil coacting therewith, and means of connection beas to tip it to an angular position with the rigid means moving said hammer away from said portion of said housing upon predetermined resistance to driving torque.

tween the other of said end membersand said 5. In an impact tool, a housing, a driven shaft projecting into said housing, a tool rotating shaft projecting from said housing and an operative connection within said housing between said shafts comprising a rotary anvil carried by said tool shaft, a, rotary hammer for coaction there-v with, and means for disengaging said hammer from said anvil upon a predetermined resistance torque of the work driven by said toolrotating shaft, said last means comprising a spring biasing said hammer toward engagement with said anvil, shoe elements between a portion ofl said housingand said hammer, said driven shaft having a projection coacting with a lateral point of said shoe element to thereby cause the shoe element to lift said hammer away'yfrom said housing portion to disengage the hammer from said anvil y to thereby permit the hammer to deliver an impact blow to said anvil.

thrust plate and saidv hammer end member to release the hammer from the anvil and permit rotation of the hammer and repositioning of the shoes after disengagement of the hammer from the anvil followed by an impact blow ofthe hammer against the anvil.

9. A device for accumulating torsional force in an impact tool comprising a housing, a driven member and a hammer member therein,'resilient means interposed between said members and operable to resist movement of said members tothe hammer member and repositioning of the shoes after disengagement of the hammer membei? from the anvil followed by an impact blow of the hammer against the anvil.

10. In an impact tool, a hammer and an anvil having clutch lug engagement with each other,

a spring urging said hammer and anvil relatively toward each other to eiiect such engagement, shoes normally assuming a POSition permitting interengagement of the clutch lugs and upon cooking of the shoes as a result of greater torque being imparted to the hammer and shoes than the resistance torque of the anvil effecting disengagement and subsequent re-engagement of the clutch lugs for imparting impact blows, and driving means for said shoes and connected therewith to eiect such cooking when the driving torque is enough greater than the resistance torque to compress said spring.

1l. In an impact wrench, a housing, a driven shaft projecting into said housing, a tool shaft projecting from said housing and an operative connection between said shafts comprising a rotary anvil carried by said tool shaft, a, rotary hammer therefor, and means for disengaging said hammer from said anvil upon a predetermined resistance torque being oiered to rotation of said tool shaft, said last means comprising a spring biasing vsaid hammer toward engagement with said 'anvil and elongated separating elements normally' lying between said hammer and said anvil, said separating elements having lateral arms to coact with said driven shaft and be tilted thereby out of their normal positions to cause them to move said hammer away from said anvil upon such resistance totorque being offered.

12. In a tool of the character described, a rotary driving head, a hammer spaced from said head, coacting clutch members on said hammer and head, a driven shaft, an operative connection between said shaft and hammer which enables the head to remain stationary during a partial revolution of the hammer followedby an impact blow of the hammer against the head, a spring normally tending to engage said head and hammer, elongated separating elements lying between said hammer and said head, said elements hav-` ing lateral arms, provided with openings, a cross of the shoes with a consequent movement of said hammer away from said opposition plate resulting in separation of said hammer from said anvil upon predetermined driving torque in excess of resistance to turning torque by the work.

14. In a tool of the character described, a housing, a pair of rotatable members therein disposed substantially coaxially with relation to each other, means releasably engaging the two members intermittently including engageable clutch faces, means for effecting intermittent release and re-engagement of said clutch faces by relative movement of said members axially, rotating means to impart energy to one of said members, and means for building up energy by momentum in one of said members while said members are out of engagement to be expended upon the other member upon a subsequent re-engagement therewith to drive such last mentioned member by impact through a working stroke, sa'idlast means comprising shoes between said housing and one of said members, said rotating means being connected with said shoes laterally thereof to effect cooking of the shoes between said housing and said member to disengage the members relative to each other.

l5. In a rotary impact wrench having an anvil and a floating hammer for striking the anvil, means normally tending to hold said hammer in driving engagement with said. anvil, driving means for said hammer, and means connecting the hammer and driving means comprising otherthan-round shoes rotatable with vsaid hammer and interposed between it, and said housing, and means engageable with said shoes at points spaced from axes of oscillation of the shoes thereby to effect a change in the angular position of the shoes with a consequent movement of said hampin in said head extending into said openings for i propelling said separating elements to a tipped position when the work imposes a greater resistance torque to rotation of said head than the driving torque imparted to said separating elements by said cross pin.

13. Ina rotary impact wrench` having an anvil mer away from said housing and resulting in separation of said hammer from said anvil upon predetermined driving torque in excess of resistance to turning torque by the work.

16. In a rotary impact wrench having an anvil and a floating hammer for striking the anvil, means normally tending to hold said hammer in driving engagement with said anvil, driving means for said hammer, and means connecting the hammer and driving means comprising substantially rectangular shoes rotatable with said CLIFFORD E. FITCH. 

